Photographic lenses used for a camera are grouped into multiple lens groups. The lens groups are configured to change the distances in an optical axis between the lens groups in order to fulfill their functions including a focusing function, a zooming function or smooth focal-length changing function, and a retracting function. Particularly, in a photographic lens having a zooming function and/or a retracting function, the distance each lens group moves is so long that the configuration of the lens barrel is complicated.
There has recently been demands that photographing apparatuses such as digital cameras should deliver higher performance with a zooming function to provide high-quality images, and that the photographing apparatuses also should be reduced in size for the purpose of improving their portability. Advancement of technical development has been satisfying those demands. A retractable lens barrel is an effective solution for satisfying the demand for the size reduction of photographing apparatuses. For this reason, a growing number of cameras each having a retractable lens barrel are used. However, in the case where a lens barrel adapted for a retractable camera simply move and retrace the whole lens groups constituting the lens system in the optical axis direction, this design poses a limit on reduction of the length of the whole lens barrel in the retracted state, and accordingly imposes a restriction on constructing thinner camera main bodies.
With this taken into consideration, a photographing apparatus of a type including a mechanism for withdrawing some of the lens groups from the optical axis, and concurrently for retracting the rest of the lens groups in the optical axis direction, has been proposed and thus put into practical use. An example of this case is an invention which has been made by the inventor of the present invention, and which is disclosed in Japanese Patent Application Publication No. 2006-39152. In the case of the invention disclosed in Japanese Patent Application Publication No. 2006-39152, a cam groove is formed in an inner surface of a fixation frame to have its own object-side end portion in parallel with an end surface of a fixation cylinder.
With this configuration, by being engaged with a cam follower of a first revolvable cylinder, the cam groove extracts the first revolvable cylinder to the maximum exaction position while driving the lens groups from the retracted position to the short-focal-point/wide-angle end, and then idly revolves the first revolvable cylinder while driving the lens groups from their short-focal-point/wide-angle end to their long-focal-point/telephoto end. In other words, this cam groove is made for a withdrawn third lens group to quickly advance onto the optical axis by extracting the first revolvable cylinder fully in an earlier phase of the operation for extracting the lens groups, and thereby by securing a space for a frame of the third lens group to be inserted onto the optical axis.
It is necessary that, among the photographic lenses, lens groups movable in the optical axis direction should be firmly held at their stop position. Particularly in the case of the lens barrel adapted for the retractable camera, the lens groups move such long distances that it is difficult to firmly hold the lens groups at their respective stop positions no matter what positions the lens groups may stop at. The reason for this difficulty is that there is a gap between a straight advancement guiding groove and the cam follower as well as a gap between the cam groove and the cam follower in the lens barrel using a lens group moving mechanism, which includes the straight advancement guiding groove and the cam groove crossing the straight advancement guiding groove as a mechanism for moving the lens groups in long distances, and which is constructed by fitting the cam follower integrated with the lens groups into an intersection between the above-mentioned straight advancement guiding groove and the cam groove.
This is because, although as a mechanism for moving lens groups in long distances used is a lens moving mechanism including a straight advancement guiding groove and a cam groove crossing the straight advancement guiding groove, and configured by fitting a cam follower integrated with the lens groups into an intersection between the straight advancement guiding groove and the cam groove, this mechanism inevitably has a gap, which is even a very slight gap, between the cam groove and each of the straight advancement guiding groove and the cam groove.
The lens groups move in these gaps, which makes the positions of the lenses unstable. Such instability puts the lenses out of focus as well as reduces the resolution of the lenses. This kind of problem is not peculiar to the invention disclosed in Japanese Patent Application Publication No. 2006-39152, but is common among retractable cameras and among lens barrels each including the lens moving mechanism having the cam groove and the cam follower.